This invention relates to feedthroughs for providing an electrical path for implantable medical devices including electrical pulse generators. Examples of such devices are implantable cardiac pacemakers and implantable cardiac defibrillators for correction of cardiac abnormalities. The pacemaker or defibrillator device has a housing containing a pulse generator including associated circuitry and a battery that serves as a power supply. A conductive lead or pin extends from the pulse generator circuit in the interior of the device and passes through the device housing where it is connected via a medical lead to an electrode surgically attached to an appropriate location in the heart.
One of the concerns related to the use of such implantable medical devices (pacemakers, defibrillators, etc.) is that they are subject to stray electromagnetic interference (EMI). Such EMI may come from sources such as television transmitters, cell phones, theft detection devices and so on. This spurious EMI is highly undesirable because it can interfere with proper functioning of the implanted medical device, either by inhibiting a proper response or by causing an improper one. Such stray EMI can essentially be eliminated as a problem source by shunting the EMI to ground with the use of a filter capacitor connected between the input lead wire(s) and electrical ground. Typically, one capacitor is positioned between each such lead wire and ground. These capacitors are often built into a monolithic structure or array when used for a multilead feedthrough. If the array is in the form of a right circular cylinder, it is designated a discoidal capacitor.
However, these prior art type feedthroughs routinely use conductive polymeric materials such as polyimides and epoxies or metallic materials such as solder alloys for holding their constituent parts together. Use of the conductive polymeric materials requires care in preventing leakage of the conductive polymer into locations in the assembly where it could cause a short circuit rendering the implantable medical device inoperative. In addition, conductive polymers exhibit relatively low electrical conductivity as compared with metallic materials. The bonding mechanism between the conductive polymer and the metallic members of the feedthrough is predominately mechanical, resulting in a relatively weak electrical and mechanical connection. Solders have relatively low melting temperatures such that subsequent high temperature welding operations on other parts of the device can compromise the soldered joint or cause beading in which a ball or pellet of solder could fall into a location in the device where a short circuit could result. Additionally, some soldering operations require the use of fluxes that leave behind undesirable residues after the soldering is completed and that can be a source of entrapped moisture, possibly resulting in device failure. Thus, there is a need for a better filtered feedthrough device as well as a better filtered feedthrough assembly process.